Low-power wireless diversity receiver with multiple receive paths

ABSTRACT

A low-power diversity receiver includes at least two receive paths, each of which is designated as a primary or secondary receive path. A primary receive path is compliant with system requirements (e.g., IS-98D requirements). A secondary receive path is not fully compliant with the system requirements and is designed for lower power, less area, and lower cost than the primary receive path. For a multi-antenna receiver, the two receive paths may be used to simultaneously process two received signals from two antennas. For a single-antenna receiver, either the primary or secondary receive path is selected, e.g., depending on whether or not large amplitude “jammers” are detected, to process a single input signal from one antenna. The receiver may include additional receive paths for additional frequency bands and/or GPS.

The present application for patent claims priority to ProvisionalApplication No. 60/531,241, entitled “Low-Power Wireless DiversityReceiver with Multiple Receive Paths” filed Dec. 18, 2003, and assignedto the assignee hereof and hereby expressly incorporated by referenceherein.

BACKGROUND

I. Field

The present invention relates generally to electronics, and morespecifically to a diversity receiver for wireless communication.

II. Background

In a wireless communication system, a transmitter modulates data onto aradio frequency (RF) carrier signal to generate an RF modulated signalthat is more suitable for transmission. The transmitter then transmitsthe RF modulated signal via a wireless channel to a receiver. Thetransmitted signal may reach the receiver via one or more propagationpaths (e.g., a line-of-sight path and/or reflected paths). Thecharacteristics of the propagation paths may vary over time due tovarious phenomena such as fading and multipath. Consequently, thetransmitted signal may experience different channel conditions and maybe received with different amplitudes and/or phases over time.

To provide diversity against deleterious path effects, multiple antennasmay be used to receive the RF modulated signal. At least one propagationpath typically exists between the transmit antenna and each of thereceive antennas. If the propagation paths for different receiveantennas are independent, which is generally true to at least an extent,then diversity increases and the received signal quality improves whenmultiple antennas are used to receive the RF modulated signal.

A multi-antenna receiver conventionally has one RF receiver processingpath (or simply, “receive path”) for each receive antenna. Each receivepath includes various circuit blocks (e.g., amplifiers, filters, mixers,and so on) used to condition and process a received signal from anassociated antenna. The circuit blocks are designed to meet varioussystem requirements such as linearity, dynamic range, sensitivity,out-of-band rejection, and so on, as is known in the art. Inconventional diversity receiver designs, the receive path is typicallyreplicated for each receive antenna. The replication of the receivepaths with identical circuitry results in higher power consumption,larger area, and higher cost for the multi-antenna receiver, all ofwhich are undesirable. For a portable wireless device, the higher powerconsumption adversely impacts standby time and reduces talk time betweenbattery recharges.

There is therefore a need in the art for a low-power diversity receiver.

SUMMARY

A low-power diversity receiver having good performance is describedherein. The diversity receiver includes two or more receive paths, eachof which is designated as a primary or secondary receive path. A primaryreceive path is compliant with applicable system requirements (e.g.,IS-98D, cdma2000, GSM and/or W-CDMA requirements). A secondary receivepath is designed for low power but is not fully compliant with thesystem requirements. For example, the secondary receive path may bedesigned to meet requirements for dynamic range and sensitivity but notfor certain out-of-band rejection of large amplitude “jammers”, whichare undesired signals outside of the RF channel of interest. The relaxedrequirements allow the secondary receive path to be implemented withlower power consumption, less area, and lower cost. The second receivepath can provide good performance under most operating conditions. For amulti-antenna receiver, the primary and secondary receive paths may beused to simultaneously process two received signals from two antennas.For a single-antenna receiver, either the primary or secondary receivepath may be selected, e.g., depending on whether or not jammers aredetected, to process a single received signal from one antenna.

In an exemplary embodiment, a wireless device with two receive paths forone frequency band is described. The first (primary) receive pathincludes (1) a first amplifier that amplifies a first input signal andprovides a first amplified signal and (2) a first downconverter thattranslates the first amplified signal in frequency (e.g., from RF downto baseband) and provides a first baseband signal. The second(secondary) receive path includes (1) a second amplifier that amplifiesa second input signal and provides a second amplified signal and (2) asecond downconverter that translates the second amplified signal infrequency and provides a second baseband signal. The first receive pathis compliant with system requirements, and the second receive path isnon-compliant with some or all of the system requirements. A jammerdetector detects for the presence of large amplitude jammers in thefirst and/or second input signal. If only one receive path is needed,then the first receive path is selected if jammers are detected and thesecond receive path is selected for use if jammers are not detected. Thewireless device may include additional receive paths for additionalfrequency bands and/or GPS.

Various aspects and embodiments of the invention are described infurther detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and nature of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings in which like reference charactersidentify correspondingly throughout and wherein:

FIG. 1 shows a wireless communication system;

FIG. 2 shows a single-antenna terminal with two receive paths;

FIG. 3 shows a dual-antenna terminal with two receive paths;

FIG. 4 shows a dual-antenna terminal with five receive paths for twofrequency bands and GPS;

FIG. 5 shows a dual-path receiver with a direct-to-basebandarchitecture;

FIG. 6 shows a dual-path receiver with a super-heterodyne architecture;

FIGS. 7 and 8 show two dual-path receivers that may also be used for thedual-antenna terminal in FIG. 3;

FIG. 9 shows a lowpass filter;

FIG. 10 shows a jammer detector; and

FIG. 11 shows a process for operating two receive paths in a wirelessterminal.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment or design described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs.

FIG. 1 shows a wireless communication system 100 in which a number ofwireless terminals communicate with a number of base stations. Forsimplicity, only two terminals 110 a and 110 b and two base stations 120a and 120 b are shown in FIG. 1. Each terminal 110 may receive signalsfrom any number of transmitting sources at any given moment vialine-of-sight paths and/or reflected paths. A reflected path is createdwhen a transmitted signal reflects off a reflection source (e.g., abuilding, tree, or some other obstruction) and arrives at the terminalvia a different path than the line-of-sight path. A terminal may also bereferred to as a remote station, a mobile station, an access terminal, auser equipment (UE), a wireless communication device, a cellular phone,or some other terminology. Terminal 110 a is equipped with a singleantenna, and terminal 110 b is equipped with two antennas. A basestation is a fixed station and may also be referred to as an accesspoint, a Node B, or some other terminology. A mobile switching center(MSC) 140 couples to the base stations and provides coordination andcontrol for these base stations.

A terminal may or may not be capable of receiving signals fromsatellites 130. Satellites 130 may belong to a satellite positioningsystem such as the well-known Global Positioning System (GPS). Each GPSsatellite transmits a GPS signal encoded with information that allowsGPS receivers on earth to measure the time of arrival of the GPS signal.Measurements for a sufficient number of GPS satellites can be used toaccurately estimate a three-dimensional position of a GPS receiver. Aterminal may also be capable of receiving signals from other types oftransmitting sources such as a Bluetooth transmitter, a wireless localarea network (WLAN) transmitter, an IEEE 802.11 (Wi-Fi) transmitter, andso on.

In FIG. 1, each terminal 110 is shown as receiving signals from multipletransmitting sources simultaneously, where a transmitting source may bea base station or a satellite. In general, a terminal may receivesignals from zero, one, or multiple transmitting sources at any givenmoment. For multi-antenna terminal 110 b, the signal from eachtransmitting source is received by each of the multiple antennas at theterminal, albeit at different amplitudes and/or phases.

System 100 may be a Code Division Multiple Access (CDMA) system, a TimeDivision Multiple Access (TDMA) system, or some other wirelesscommunication system. A CDMA system may implement one or more CDMAstandards such as IS-95, IS-2000 (also commonly known as “1x”), IS-856(also commonly known as “1xEV-DO”), Wideband-CDMA (W-CDMA), and so on. ATDMA system may implement one or more TDMA standards such as GlobalSystem for Mobile Communications (GSM). The W-CDMA standard is definedby a consortium known as 3GPP, and the IS-2000 and IS-856 standards aredefined by a consortium known as 3GPP2. These standards are known in theart.

Low-power diversity receivers that can provide good performance aredescribed herein. A diversity receiver is a receiver with at least tworeceive paths, with each receive path being capable of conditioning(e.g., amplifying and/or filtering) an RF signal and frequencydownconverting the signal to baseband. The low-power diversity receiversmay be used for terminals with a single antenna as well as terminalswith multiple antennas. Some exemplary low-power diversity receivers aredescribed below.

FIG. 2 shows a block diagram of an embodiment of single-antenna terminal110 a. In this embodiment, terminal 110 a includes a single antenna 212and two receive paths 220 a and 220 b. Antenna 212 receives RF modulatedsignals from base stations 120 and provides a received signal (Prx) thatincludes versions of the RF modulated signals transmitted by these basestations. A low noise amplifier (LNA) 216 performs low noiseamplification on the received signal and provides an input signal (Pin)to both receive paths 220 a and 220 b. Receive path 220 a is designatedas the primary receive path, and receive path 220 b is designated as thesecondary receive path.

Each receive path 220 processes the input signal from LNA 216 andprovides a respective output baseband signal. Receive path 220 a isdesigned to meet applicable system requirements (e.g., for sensitivity,dynamic range, linearity, out-of-band rejection, and so on) and may beused for all operating conditions. Receive path 220 b is designed forlow power and with less stringent requirements and may be used for mostoperating conditions. Exemplary designs for receive paths 220 a and 220b are described below.

An analog-to-digital converter (ADC) 230 a receives and digitizes thefirst output baseband signal (Pout1) from receive path 220 a andprovides a first stream of data samples to a data processor 240 forfurther processing. Similarly, an ADC 230 b receives and digitizes thesecond output baseband signal (Pout2) from receive path 220 b andprovides a second stream of data samples to data processor 240. Althoughnot shown in FIG. 2 for simplicity, each output baseband signal and eachdata sample stream may be a complex signal/stream having an inphase (I)component and a quadrature (Q) component.

For the embodiment shown in FIG. 2, a signal detector 242 detects forthe signal level of the desired signal, which is the signal within an RFchannel of interest. The desired signal detection may be performed invarious manners known in the art. For example, an automatic gain control(AGC) loop is typically used to adjust the gains of variable gainamplifiers (VGAs) located within the receive paths so that outputbaseband signals at the proper amplitude are provided to the ADCs. Thegain control signals for these VGAs are indicative of, and may be mappedto, the desired signal level. A jammer detector 250 receives a firstdetector input signal (D1) from receive path 220 a and a second detectorinput signal (D2) from receive path 220 b, detects for the presence oflarge amplitude jammers in the received signal, and provides a jammerstatus signal indicating whether or not large amplitude jammers arepresent in the received signal. A control unit 252 receives the jammerstatus signal from jammer detector 250 and a Mode control signal fromdata processor 240 and provides the Enb1 and Enb2 signals used to enablereceive paths 220 a and 220 b, respectively. For example, control unit252 may select (1) receive path 220 a if large amplitude jammers aredetected in the received signal and (2) receive path 220 b otherwise.

In one configuration, either receive path 220 a or 220 b is selected foruse at any given moment, depending on the operating conditions. Inanother configuration, both receive paths 220 a and 220 b may be activeat the same time to simultaneously process signals from two differentsystems. ADC 230 b may be omitted, and a switch may be used to providethe output baseband signal from either receive path 220 a or 220 b toADC 230 a.

FIG. 3 shows a block diagram of an embodiment of multi-antenna terminal110 b. In this embodiment, terminal 110 b includes two antennas 312 aand 312 b and two receive paths 320 a and 320 b. The two antennas 312 aand 312 b may be formed in various manners at terminal 110 b (e.g., withprinted traces on a circuit board, wire conductors, and so on), as isknown in the art. An LNA 316 a amplifies a first received signal (Prx)from antenna 312 a and provides a first input signal (Pin) to receivepath 320 a. Similarly, an LNA 316 b amplifies a second received signal(Srx) from antenna 312 b and provides a second input signal (Sin) toreceive path 320 b. Receive path 320 a is designated as the primaryreceive path, and receive path 320 b is designated as thesecondary/diversity receive path. LNAs 316 a and 316 b may also beconsidered as part of receive paths 320 a and 320 b, respectively.

Each receive path 320 processes the input signal from one LNA 316 andprovides a respective output baseband signal. Receive path 320 a isdesigned to meet applicable system requirements and may be used for alloperating conditions. Receive path 320 b is designed for low power andwith less stringent requirements and may be used for most operatingconditions. In one configuration, either receive path 320 a or 320 b isselected for use at any given moment, depending on the operatingconditions. In another configuration, both receive paths 320 a and 320 bare active at the same time to simultaneously process two receivedsignals for the same wireless system in order to achieve diversity. Inyet another configuration, both receive paths 320 a and 320 bsimultaneously process signals for two different systems. Exemplarydesigns for receive paths 320 a and 320 b are described below.

ADC 330 a receives and digitizes the first output baseband signal (Pout)from receive path 320 a and provides a first data sample stream to adata processor 340. Similarly, an ADC 330 b receives and digitizes thesecond output baseband signal (Sout) from receive path 320 b andprovides a second data sample stream to data processor 340. A signaldetector 342 detects for the desired signal level. A jammer detector 350detects for the presence of large amplitude jammers in the first and/orsecond received signal and provides a jammer status signal. A controlunit 352 enables one or both receive paths 320 a and 320 b based on thejammer status signal from jammer detector 350 and the Mode controlsignal from data processor 340.

A wireless terminal may be a single-band terminal or a multi-bandterminal. A single-band terminal supports operation on one specificfrequency band. A multi-band terminal supports operation on multiplefrequency bands and typically operates on one of the supported bands atany given moment. A multi-band terminal can communicate with differentwireless communication systems operating on different frequency bands.Table 1 lists various frequency bands commonly used for wirelesscommunication as well as the frequency band for GPS.

TABLE 1 Frequency Band Frequency Range Personal Communication System(PCS) 1850 to 1990 MHz Cellular 824 to 894 MHz Digital Cellular System(DCS) 1710 to 1880 MHz GSM900 890 to 960 MHz International MobileTelecommunications- 1920 to 2170 MHz 2000 (IMT-2000) CDMA450 411 to 493MHz JCDMA 832 to 925 MHz KPCS 1750 to 1870 MHz GPS 1574.4 to 1576.4 MHzThe PCS band is also known as GSM1900, the DCS band is also known asGSM1800, and the cellular band is also known as an Advanced Mobile PhoneSystem (AMPS) band. A wireless communication system may also operate ona frequency band that is not listed in Table 1.

For each of the frequency bands listed in Table 1 except for GPS, onefrequency range is used for the forward link (i.e., downlink) from thebase stations to the terminals, and another frequency range is used forthe reverse link (i.e., uplink) from the terminals to the base stations.As an example, for the cellular band, the 824 to 849 MHz range is usedfor the reverse link, and the 869 to 894 MHz range is used for theforward link.

FIG. 4 shows a block diagram of an embodiment of dual-band plus GPS,multi-antenna terminal 110 c (not shown in FIG. 1). Terminal 110 csupports operation on two frequency bands, which for clarity are thecellular and PCS bands in the following description. In the embodimentshown in FIG. 4, terminal 110 c includes two antennas 412 a and 412 band five receive paths 420 a through 420 e. The received signal (Prx)from antenna 412 a is provided to a diplexer 414 a, which provides afirst cellular signal to an LNA 416 a and a first PCS signal to an LNA416 b. LNAs 416 a and 416 b perform low noise amplification on theirsignals and provide Pin1 and Pin2 input signals to receive paths 420 aand 420 b, respectively. Similarly, the received signal (Srx) fromantenna 412 b is provided to a diplexer 414 b, which provides a secondcellular signal to an LNA 416 c and a second PCS signal to an LNA 416 d.LNAs 416 c and 416 d perform low noise amplification on their signalsand provide Sin1 and Sin2 input signals to receive paths 420 c and 420d, respectively. An LNA 416 e performs low noise amplification on areceived GPS signal (Grx) and provides a Gin input signal to receivepath 420 e. LNAs 416 a through 416 e may also be considered as part ofreceive paths 420 a through 420 e, respectively.

Each receive path 420 conditions and frequency downconverts its inputsignal and provides a respective baseband signal. Receive paths 420 aand 420 b are designated as primary receive paths and are designed tomeet applicable system requirements. Receive paths 420 c and 420 d aredesignated as secondary receive paths and are designed for low power andwith less stringent requirements. Receive paths 420 c and 420 d may beimplemented with circuit blocks that consume less power, occupy smallerarea, and cost less than those of receive paths 420 a and 420 b.

For the embodiment shown in FIG. 4, receive paths 420 a and 420 b sharebaseband circuit blocks, and receive paths 420 c, 420 d, and 420 e sharebaseband circuit blocks. A lowpass filter 440 a filters the basebandsignal from either receive path 420 a or 420 b and provides a firstfiltered baseband signal and the D1 detector input signal. A lowpassfilter 440 b filters the baseband signal from receive path 420 c, 420 d,or 420 e and provides a second filtered baseband signal and the D2detector input signal. Amplifiers 442 a and 442 b amplify and buffer thefirst and second filtered baseband signals and provide the first andsecond output baseband signals, Pout and Sout, respectively.

A jammer detector 450 receives the first and second detector inputsignals (D1 and D2) from lowpass filters 440 a and 440 b, respectively,detects for the presence of large amplitude jammers in the receivedsignal, and provides the jammer status signal. A control unit 452receives the jammer status signal and the Mode control signal andprovides enable signals used to enable receive paths 420 a through 420e. For example, control unit 452 may select (1) primary receive path 420a or 420 b if large amplitude jammers are present, (2) secondary receivepath 420 c or 420 d if large amplitude jammers are not present, (3) bothreceive paths 420 a and 420 c for the cellular band or both receivepaths 420 b and 420 d for the PCS band, for the diversity mode, (4)receive path 420 a or 420 b for wireless communication and receive path420 e for GPS, and so on.

Receive paths 420 a and 420 c are designed for the cellular band,receive paths 420 b and 420 d are designed for the PCS band, and receivepath 420 e is designed for GPS frequency. Receive paths 420 a and 420 bmay be implemented with narrowband circuit blocks that are tuned to thecellular and PCS bands, respectively. Receive paths 420 c and 420 d maybe implemented with narrowband and/or wideband circuit blocks to achievethe desired performance. For example, the circuit blocks in receivepaths 420 c and 420 d may be implemented with resistors or low qualityinductors, whereas the circuit blocks for receive paths 420 a and 420 bmay be implemented with high quality inductors.

The primary receive paths (receive path 220 a in FIG. 2, receive path320 a in FIG. 3, and receive paths 420 a and 420 b in FIG. 4) aredesigned to meet applicable system requirements. For CDMA, IS-98D andcdma2000 specify a two-tone test and a single-tone test. For thetwo-tone test, two tones (or jammers) are located at +900 KHz and +1700KHz (or at −900 KHz and −1700 KHz) from the center frequency of a CDMAwaveform and are 58 dB higher in amplitude than the CDMA signal level.For the single-tone test, a single tone is located at +900 KHz from thecenter frequency of the CDMA waveform and is 72 dB higher in amplitudethan the CDMA signal level. These tests define the linearity and dynamicrange requirements for the receive path. In most systems, jammers arepresent for only a small fraction of the time and rarely reach the +58or +72 dB level as specified by IS-98D and cdma2000. Nevertheless, theprimary receive paths may be designed to be IS-98D and cdma2000compliant so that they can provide the specified performance for alloperating conditions.

The secondary receive paths (receive path 220 b in FIG. 2, receive path320 b in FIG. 3, and receive paths 420 c and 420 d in FIG. 4) aredesigned to be low-power and with less stringent requirements. Forexample, the secondary receive paths may be designed to meet dynamicrange and sensitivity requirements, albeit assuming that large amplitudejammers are not present in the received signal. With the relaxedrequirements, the secondary receive paths may be designed to consumeonly a fraction (e.g., 50% or 25%) of the power consumed by thecorresponding primary receive paths. The secondary receive paths canstill provide good performance most of the time since large amplitudejammers are present intermittently. The secondary receive paths canprovide substantial power savings if they are used in place of theprimary receive paths.

When not operating in the diversity mode, either the primary orsecondary receive path is selected for use depending on one or morecriteria. These criteria may include (1) presence or absence of largeamplitude jammers in the received signal and (2) the desired signallevel. Table 2 shows an embodiment for selecting receive path basedsolely on jammer detection.

TABLE 2 Jammers Receive Path Present in the received signal Primaryreceive path Not present in the received signal Secondary receive pathTable 3 shows an embodiment for selecting receive path based on jammerdetection and desired signal level.

TABLE 3 Jammers Desired Signal Receive Path Present Weak Primary receivepath Present Strong Secondary or primary receive path depending on powerlevel of jammer Not present Weak Secondary receive path Not presentStrong Secondary receive pathLarge amplitude jammers may be deemed to be present in the receivedsignal if their signal level exceeds a particular threshold, asdescribed below. The desired signal may be deemed to be strong if itexceeds a particular signal level. This signal level may be dependent onthe actual performance of the secondary path and may be circuit andimplementation dependent. The selection of receive path may also bebased on other criteria (e.g., received signal quality orsignal-to-noise ratio (SNR), pilot received signal strength, powercontrol bits, and so on), and this is within the scope of the invention.

A receive path may be implemented with a super-heterodyne architectureor a direct-to-baseband architecture. In the super-heterodynearchitecture, the received signal is frequency downconverted in multiplestages, e.g., from RF to an intermediate frequency (IF) in one stage,and then from IF to baseband in another stage. In the direct-to-basebandarchitecture, the received signal is frequency downconverted from RFdirectly to baseband in one stage. The super-heterodyne anddirect-to-baseband architectures may use different circuit blocks and/orhave different circuit requirements.

FIG. 5 shows a block diagram of a dual-path receiver 500, whichimplements the direct-to-baseband architecture and may be used for bothsingle-antenna terminal 110 a and multi-antenna terminal 110 b inFIG. 1. Receiver 500 includes two receive paths 520 a and 520 b that maybe used for receive paths 220 a and 220 b, respectively, in FIG. 2. Inthis case, both receive paths 520 a and 520 b are provided with the sameinput signal, Pin (not shown in FIG. 5). Receive paths 520 a and 520 bmay also be used for receive paths 320 a and 320 b, respectively, inFIG. 3. In this case, receive paths 520 a and 520 b are provided withdifferent input signals, Pin and Sin, respectively, as shown in FIG. 5.The RF portion of receive paths 520 a and 520 b may be used for receivepaths 420 a and 420 c, respectively, and for receive paths 420 b and 420d, respectively, in FIG. 4, as described below. Receive path 520 a isthe primary receive path, and receive path 520 b is thesecondary/diversity receive path.

Within receive path 520 a, a VGA 524 a amplifies the input signal (Pin)with a first variable gain (Gp1). A filter 526 a filters the signal fromVGA 524 a to pass signal components in the band of interest and removeout-of-band noise and undesired signals. For two-way communication,signals are transmitted simultaneously on the forward link and reverselink. The transmitted signal sent by the terminal on the reverse link istypically much larger in amplitude than the received signal for theforward link. Filter 526 a may pass the RF components for the receivefrequency range (e.g., from 869 to 894 MHz for cellular band) and filterout and suppress the RF components for the transmit frequency range(e.g., from 824 to 849 MHz for the cellular band). Filter 526 a may thushave a passband that corresponds to an entire frequency range/band ofinterest (e.g., cellular). Because of the potentially large differencein the transmit and receive signal levels, filter 526 a needs to providea large amount of out-of-band rejection in order to meet systemrequirements. Filter 526 a may be implemented with a surface acousticwave (SAW) filter (which has a sharp roll-off and is often used forapplications requiring large attenuation of out-of-band signals), aceramic filter, or some other type of filter.

A VGA 528 a amplifies the signal from filter 526 a with a secondvariable gain (Gp2) and provides a first conditioned signal having thedesired signal level. VGAs 524 a and 528 a provide the requiredamplification for the Pin signal, which may vary by 90 dB or more.Additional gain may be provided by other circuit blocks in the receivepath. A downconverter 530 a receives and frequency downconverts thefirst conditioned signal with a first LO signal and provides a firstbaseband signal. The frequency of the first LO signal is selected suchthat the signal component in the RF channel of interest is downconvertedto baseband or near-baseband. For CDMA, each frequency band covers manyRF channels, and each RF channel has a bandwidth of 1.23 MHz. A wirelessterminal typically receives signal on one RF channel at any givenmoment.

A lowpass filter 540 a filters the first baseband signal to pass thesignal components in the RF channel of interest and to remove noise andundesired signals that may be generated by the downconversion process.For the direct-to-baseband architecture, filter 526 a may pass theentire frequency band of interest, and lowpass filter 540 a would thenpass the RF channel of interest. Lowpass filter 540 a may be implementedwith various filter types (e.g., Butterworth, elliptical, Chebychev, andso on), with the proper filter order and bandwidth, and with sufficientbias current to meet linearity and dynamic range requirements. Lowpassfilter 540 a provides a first filtered baseband signal and the D1 signalfor the jammer detector. An amplifier 542 a amplifies and buffers thefirst filtered baseband signal and provides the first output basebandsignal (Pout).

An LO generator 546 a provides the first LO signal used to downconvertthe Pin signal from RF to baseband. LO generator 546 a may beimplemented with a voltage controlled oscillator (VCO) or some othertype of oscillator. The frequency of the LO signal is selected such thatthe signal component in the RF channel of interest is downconverted tobaseband or near-baseband. A phase locked loop (PLL) 548 a receives thefirst LO signal and generates a control signal for LO generator 546 asuch that the frequency and/or phase of the first LO signal is locked toa reference signal (not shown in FIG. 5).

Receive path 520 b processes the Sin signal and provides the secondoutput baseband signal (Sout), in similar manner as receive path 520 a.For each receive path, the frequency downconversion may be performed invarious manners. For example, frequency downconversion may be performedby mixing the RF input signal down to baseband, as shown in FIG. 5. Thefrequency downconversion may also be performed by sampling or digitizingthe RF input signal and using the aliasing property of data sampling togenerate samples at baseband. Frequency downconverters 530 a and 530 bmay be implemented with mixers, ADCs, mixer (e.g., for downconverter 530a) and ADC (e.g., for downconverter 530 b), and so on. RF sampling maybe more readily implemented on the secondary receive path 520 b sincethe specifications are simpler.

FIG. 5 shows a specific design for receive paths 520 a and 520 b. Ingeneral, a receive path may perform signal conditioning using one ormore stages of amplifier, filter, mixer, and so on, which may bearranged in a different manner from that shown in FIG. 5. Moreover, areceive path may employ other circuit blocks not shown in FIG. 5 forsignal conditioning.

FIG. 5 shows receive paths 520 a and 520 b having the same circuitblocks. However, different circuit designs may be used for the circuitblocks in receive paths 520 a and 520 b because of the differentrequirements and objectives for the primary and secondary receive paths.

Receive path 520 a is designed to meet applicable system requirements,e.g., linearity, dynamic range, and sensitivity requirements. To achievethis, the RF circuit blocks in receive path 520 a are typicallynarrowband circuits tuned to a specific frequency band (e.g., cellularor PCS band). For example, VGAs 524 a and 528 a and downconverter 530 amay be implemented with narrowband circuits to achieve the desiredlinearity over a wide dynamic range. The narrowband circuit blocks mayuse matching and tuned circuits, inductive degeneration, and othercircuit techniques known in the art to achieve the desired performance.Lowpass filter 540 a may be designed with a relatively sharp roll-off(e.g., as a 5-th order elliptical filter) in order to attenuate largeamplitude jammers in the input signal. These jammers can take up a largeportion of the dynamic range of the subsequent ADC if they are notsufficiently filtered. LO generator 546 a is designed to have good phasenoise performance. In general, good performance for the circuit blockswithin receive path 520 a typically requires the use of larger-sizecircuit components (e.g., larger capacitors, inductors and/ortransistors) and large amounts of bias current.

Receive path 520 b is designed for low-power and with less stringentrequirements, which assumes that large amplitude jammers are not presentin the received signal. Because of the less stringent requirements, VGAs524 b and 528 b, downconverter 530 b, filter 540 b, and amplifier 542 bmay be designed with smaller-size circuit components (e.g., smallercapacitors) and smaller amounts of bias current. VGAs 524 b and 528 band downconverter 530 b may be implemented without using inductors(which typically occupy a large area) or by using inductors of lowerquality (which can occupy a smaller area). Filter 526 b may beimplemented with on-chip circuit components instead of an external SAWfilter (which may be needed for filter 526 a). Because large amplitudejammers are assumed to be absent for receive path 520 b, the overallgain may be distributed differently for the secondary receive path in amanner to further reduce power consumption, area, and cost. Lowpassfilter 540 b may be implemented with a lower order (e.g., as a 3-rdorder elliptical filter) than lowpass filter 540 a. Using these variouscircuit design techniques, receive path 520 b may be designed to consumeonly a fraction (e.g., 50% or 25%) of the power and occupy only a smallfraction of the area required by receive path 520 a.

FIG. 6 shows a block diagram of a dual-path receiver 600, whichimplements the super-heterodyne architecture and may also be used forboth single-antenna terminal 110 a and multi-antenna terminal 110 b.Receiver 600 includes two receive paths 620 a and 620 b that may be usedfor receive paths 220 a and 220 b, respectively, in FIG. 2, and forreceive paths 320 a and 320 b, respectively, in FIG. 3. The RF portionof receive paths 620 a and 620 b may be used for receive paths 420 a and420 c, respectively, and for receive paths 420 b and 420 d,respectively, in FIG. 4.

Within receive path 620 a, the input signal (Pin) is amplified by a VGA614 a, filtered by a filter 616 a, and downconverted from RF to IF by afrequency downconverter 622 a. The IF signal from downconverter 622 a isfurther amplified by a VGA 624 a, filtered by a bandpass filter 626 a,amplified and buffered by an amplifier 628 a, and downconverted from IFto baseband by a frequency downconverter 630 a. The baseband signal fromdownconverter 630 a is filtered by a lowpass filter 640 a and amplifiedand buffered by an amplifier 642 a to obtain the first output basebandsignal (Pout).

For the super-heterodyne architecture, bandpass filter 626 a may beimplemented with a SAW filter and may perform RF channel selection(i.e., may have a passband corresponding to one RF channel, instead ofan entire frequency band). If the RF channel selection is performed bybandpass filter 626 a, then the requirements for lowpass filter 640 amay be relaxed.

An LO generator 646 a provides a first LO signal used for RF to IFdownconversion and a second LO signal used for IF to basebanddownconversion. Typically, the IF is fixed, the frequency of the firstLO signal is selected such that the signal component in the RF channelof interest is downconverted to the fixed IF, and the frequency of thesecond LO signal is also fixed.

Receive path 620 b processes the Sin signal and provides the secondoutput baseband signal (Sout), in similar manner as receive path 620 a.Receive path 620 b may be implemented with circuit blocks that consumeless power, occupy smaller area, and are lower cost than those ofreceive path 620 a.

Referring back to FIG. 4, receive paths 420 a through 420 e may beimplemented with the direct-to-baseband architecture or thesuper-heterodyne architecture. For the direct-to-baseband architecture,each of receive paths 420 a through 420 e may be implemented with VGAs524 and 528, filter 526, and frequency downconverter 530 in FIG. 5. Forthe super-heterodyne architecture, each of receive paths 420 a through420 e may be implemented with VGAs 614 and 624, amplifier 628, filters616 and 626, and frequency downconverters 622 and 630 in FIG. 6.

Two LO generators operating independently, as shown in FIGS. 5 and 6,may be used for the primary and secondary receive paths. This designallows the primary and secondary receive paths to operate simultaneouslyand independently to process two signals on two different RF channels.This capability may be useful for various applications. For example, aterminal with this capability can receive two simultaneous transmissionson two RF channels from one or two systems. As another example, aterminal with this capability can perform mobile-assisted hand-off(MAHO) to select the best base stations to communicate with. Theterminal can receive a transmission from a serving base station with theprimary receive path and can simultaneously search for signals fromother base stations with the secondary receive path. This would thenallow the terminal to initiate a hand-off to another base station thatis better than the serving base station, if one is found. If independentoperation of the primary and secondary receive paths is not needed, thenone LO generator may be shared by both receive paths.

Although not indicated in FIGS. 2 through 6 for simplicity, the primaryreceive paths (receive path 220 a in FIG. 2, receive path 320 a in FIG.3, receive paths 420 a and 420 b in FIG. 4, receive path 520 a in FIG.5, and receive path 620 a in FIG. 6) may be designed with multiple powermodes, e.g., a high power mode and a low power mode. In the high powermode, the circuit blocks (e.g., amplifiers, mixers, and so on) withinthe primary receive paths may be biased with high current to meetapplicable system requirements under the worst-case operating condition,such as those specified by IS-98D or cdma2000. In the low power mode,the circuit blocks within the primary receive paths may be biased withless current that can still meet applicable system requirements undermore moderate operating condition, e.g., with no jammers or lowamplitude jammers. The primary receive paths may also be designed withmore than two power modes, with more current being used for more severeoperating condition.

Many wireless systems have an open loop transmit power specificationthat dictates the amount of transmit power to use at the start of atransmission based on the received power level. A terminal typicallydoes not know the transmit power level needed for reliable communicationwhen the terminal is first powered on or first starts to transmit. Inthis case, the forward and reverse links may be assumed to be reciprocalof one another, i.e., the path loss for the reverse link is assumed tobe equal to the path loss for the forward link. The terminal canestimate the path loss for the forward link based on a pilot receivedfrom a base station and can determine the amount of transmit power touse for the reverse link transmission based on the forward linkmeasurement. However, if the terminal is equipped with multipleantennas, then the received power level may change abruptly whendifferent antennas are selected for use. This open loop powerdisturbance may result in the wrong transmit power level being used forthe reverse link transmission.

FIG. 7 shows a block diagram of a dual-path receiver 700 that may beused for dual-antenna terminal 110 b in FIG. 3. Receiver 700 includestwo receive paths 720 a and 720 b. Receive path 720 a is the primaryreceive path and couples to a duplexer 714 a, which further couples to atransmitter unit (TMTR) 710 and an antenna 712 a. Duplexer 714 a routesthe transmit signal from transmitter unit 710 to antenna 712 a andfurther routes the received signal from antenna 712 a to receive path720 a. Receive path 720 b is the secondary receive path and couples to aSAW filter 714 b, which further couples to an antenna 712 b. For thisembodiment, the terminal only transmits from antenna 712 a and notantenna 712 b. Antenna 712 a may be a whip/dipole antenna or some othertype of antenna. Antenna 712 b may be an internal antenna, a printedantenna, or some other type of antenna.

Receive path 720 a includes an LNA 716 a, a switch 722 a, a filter 726a, a VGA 728 a, a frequency downconverter 730 a, a lowpass filter 740 a,and an amplifier 742 a, all of which function as described above forFIGS. 2 through 6. Receive path 720 b includes the same circuit blocksas receive path 720 a. The circuit blocks for receive path 720 a may bedesigned and biased to be spec-compliant, and the circuit blocks forreceive path 720 b may be designed and biased for low power. The circuitblocks for receive path 720 a may also be designed with multiple powermodes, as described above.

In a first operating mode, both receive paths 720 a and 720 b areselected for use to achieve diversity. For this mode, switches 722 a and722 b are both switched to the “A” position and pass the output of LNAs716 a and 716 b, respectively, to filters 726 a and 726 b, respectively.If diversity is not needed, then either receive path 720 a or 720 b maybe selected for use depending on the operating condition. In a secondoperating mode, receive path 720 a is selected for use if largeamplitude jammers are detected. For this mode, switch 722 a is switchedto the “A” position, and the entire receive path 720 b may be powereddown. In a third operating mode, receive path 720 b is selected for useif no jammers or low amplitude jammers are detected. For this mode,switches 722 a and 722 b are both switched to the “B” position, and theoutput of LNA 716 a is routed to filter 726 b. LNA 716 b in receive path720 b and all of the circuit blocks after switch 722 a in receive path720 a may be powered down. LNA 716 a may also be biased with lesscurrent to conserve power. For all three operating modes, the receivedsignal power can be measured from antenna 712 a. The overall gain fromswitch 722 to amplifier 742 may be determined for each receive path andused to account for the received signal power measurements. Switches 722a and 722 b can mitigate open loop power disturbance.

FIG. 8 shows a block diagram of a dual-path receiver 702 that may alsobe used for dual-antenna terminal 110 b in FIG. 3. Receiver 702 includestwo receive paths 721 a and 721 b. Each receive path 721 includes all ofthe circuit blocks in receive path 720 in FIG. 7. However, switches 722a and 722 b are placed after filters 726 a and 726 b, respectively, inreceive paths 721 a and 721 b, respectively. If filter 726 a has betterelectrical characteristics than filter 726 b, then improved performancemay be obtained by using filter 726 a instead of filter 726 b. Ingeneral, switch 722 a may be located anywhere within receive path 721 a,and switch 722 b may be located anywhere within receive path 721 b.

FIG. 9 shows an embodiment of a lowpass filter 940, which may be usedfor each of the lowpass filters shown in FIGS. 4, 5 and 6. Lowpassfilter 940 includes a single-pole filter section 942 and bi-quad filtersections 944 and 946. Single-pole filter section 942 implements one realpole. Each of bi-quad filter sections 944 and 946 implements a pair ofcomplex poles. A 5-th order (e.g., elliptical, Butterworth, Bessel, orChebychev) filter may be implemented with all three filter sections 942,944, and 946.

The lowpass filters for the receive paths may also be implemented withother filter designs. Furthermore, the lowpass filters for the primaryand secondary receive paths may be implemented with the same ordifferent filter designs. For example, a 5-th order lowpass filter maybe used for the primary receive path, and a 3-rd order lowpass filtermay be used for the secondary receive path.

As noted above, when not operating in the diversity mode, either theprimary or secondary receive path for the desired frequency band isselected for use depending on whether or not jammers are detected in thereceived signal. Jammers are large amplitude, undesired out-of-bandsignals that can distort the desired in-band signal. The detector inputsignals used for jammer detection may be obtained from various pointsalong the receive path but should include out-of-band signal components.The detector input signals may be broadband signals with a flatfrequency response that gives equal weight to signal components atdifferent frequencies. However, jammers that are closer in-band (i.e.,closer to the desired RF channel) tend to be more detrimental to thedesired signal than jammers that are farther away in frequency. Thus,the detector input signals may be rolled off (e.g., with a first-orderlowpass filter response) to allow for discrimination of the frequencyoffset of the jammers. This would then give jammers closer in moreweight and jammers farther away less weight.

For the embodiments shown in FIGS. 4, 5 and 6, the lowpass filters alsoprovide the detector input signals (D1 and D2) used to detect for thepresence of jammers in the received signals. In an embodiment, thedetector input signals are taken after single-pole filter section 942 inthe lowpass filters.

FIG. 10 shows a block diagram of a jammer detector 1050, which may beused for the jammer detectors in FIGS. 2, 3 and 4. The D1 and D2 signalsfor the primary and secondary receive paths are rectified by rectifiers1052 a and 1052 b, filtered by lowpass filters 1054 a and 1054 b, andprovided to comparators 1056 a and 1056 b, respectively. Each rectifier1052 converts its detector input signal from a sinusoidal signal (withpositive and negative amplitude) to a single-ended signal (with onlypositive amplitude) and may be implemented with a diode. Each lowpassfilter 1054 may be implemented, for example, with a single-order lowpassfilter of an appropriate bandwidth (e.g., several hundred Hertz). Eachcomparator 1056 compares its filtered signal against a threshold level(Vth) and provides an output signal, which is (1) logic high (‘1’) ifthe filtered signal amplitude is larger than the threshold level,indicating the presence of large amplitude jammers in the receivedsignal, and (2) logic low (‘0’) otherwise. Detector logic 1058 combinesthe output signals of comparators 1056 a and 1056 b and provides thejammer status signal to control unit 252, 352, or 452.

In general, jammer detection may be performed based on (1) only the D1signal, (2) only the D2 signal, or (3) both the D1 and D2 signals. Thefiltered signals from lowpass filters 1054 a and 1054 b may be comparedagainst the threshold level as shown in FIG. 10 to obtain a 1-bit outputsignal. These filtered signals may also be digitized with an ADC toobtain multiple bits of resolution. The jammer status signal may be usedto select either the primary or secondary receive path. The jammerstatus signal may also be used to adjust (e.g., the gains and/or biascurrents of) the circuit blocks in the primary and/or secondary receivepaths.

FIG. 11 shows a flow diagram of a process 1100 for operating two receivepaths in a wireless terminal. The presence of large amplitude jammers ina first input signal or a second input signal is detected (block 1112).The first and second input signals may be from (1) one antenna for asingle-antenna terminal or (2) two antennas for a multi-antennaterminal. The primary receive path (which is spec-compliant, e.g.,IS-98D compliant) is enabled to process the first input signal if largeamplitude jammers are detected (block 1114). The secondary receive path(which is not fully spec-compliant) is enabled to process the secondinput signal if large amplitude jammers are not detected (block 1116).The primary and secondary receive paths are both enabled if themulti-antenna terminal is operating in a diversity mode and the receivedsignals from both antennas are to be processed simultaneously.Electrical characteristics (e.g., gains, bias currents, and so on) ofthe circuit blocks in the enabled receive path(s) may also be adjustedbased on the detected jammer signal level and/or the desired signallevel (block 1118).

The low-power diversity receiver described herein can provide goodperformance for both single-antenna and multi-antenna terminals undermost operating conditions. The worst-case operating condition occurswhen (1) the desired signal is near “sensitivity”, which is the lowestdetectable received signal level, and (2) the jammers are at maximumsignal level and located at a small frequency offset away from thedesired signal. This worst-case condition is a low probability event.For the single-antenna terminal, the low-power secondary receive pathmay be used for most operating conditions. For the multi-antennaterminal, the diversity mode is typically needed for only 20 to 50percent of the time. For the remaining 50 to 80 percent of the time, asingle receive path may be used, and the secondary receive path may beselected if large amplitude jammers are not detected. For bothsingle-antenna and multi-antenna terminals that are portable, thesecondary receive path consumes less power and improves both standbytime between battery recharges and talk time.

The low-power diversity receiver described herein may be used for awireless terminal to receive forward link transmissions from basestations. The low-power diversity receiver may also be used for a basestation to receive reverse link transmissions from user terminals.

The low-power diversity receiver described herein may be used forvarious wireless communication systems such as a CDMA system, a TDMAsystem, a GSM system, an AMPS system, a multiple-input multiple-output(MIMO) system, an orthogonal frequency division multiplexing (OFDM)system, an orthogonal frequency division multiple access (OFDMA) system,a wireless local area network, and so on.

A large portion of a diversity receiver (possibly all circuit blocksexcept SAW filters, control units 252, 352, and 452, and data processors240 and 340) may be implemented on one or more RF integrated circuits(RFICs). The diversity receiver may also be fabricated with various ICprocess technologies such as complementary metal oxide semiconductor(CMOS), bipolar junction transistor (BJT), bipolar-CMOS (BiCMOS),silicon germanium (SiGe), gallium arsenide (GaAs), and so on.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A multi-antenna wireless diversity receivercomprising: a first receive path having a first amplifier and a firstfrequency downconverter, operable to receive, amplify, and frequencydownconvert a first multipath of a desired signal to provide a firstbaseband signal, the first receive path having circuit blocks using highpower for high system performance; and a second receive path having asecond amplifier and a second frequency downconverter, operable toreceive, amplify, and frequency downconvert a second multipath of thedesired signal to provide a second baseband signal, the second receivepath implemented with circuit blocks that inherently consume less powerthan the circuit blocks of the first receive path, the first and secondreceive paths are interdependently alternatively enabled based directlyon a detected presence of jammer signals out-of-band and independentlyassociated with at least one of the first multipath signal and thesecond multipath signal.
 2. The device of claim 1, wherein the first andsecond receive paths concurrently process the first and second inputsignals, respectively, for diversity mode.
 3. The device of claim 1,wherein the first and second receive paths are coupled to first andsecond antennas, respectively, and wherein the device is operable tomeasure signal power of a received signal from the first antennaregardless of whether the first or second receive path is selected foruse.
 4. The device of claim 1, further comprising: a detector operativeto detect for the presence of a large amplitude of the jammer signals inthe first or second multipath signal; and a control unit operative toselect the first receive path for use if a large amplitude of the jammersignals are detected and to select the second receive path for use ifthe large amplitude of the jammer signals are not detected.
 5. Thedevice of claim 4, wherein the detector is operative to detect for thepresence of the large amplitude jammer signals based on a detector inputsignal.
 6. The device of claim 5, wherein signal components in thedetector input signal with larger frequency offsets from a desiredsignal are attenuated relative to signal components with smallerfrequency offsets from the desired signal.
 7. The device of claim 6,wherein the signal components in the detector input signal areattenuated by a first-order low pass filter response.
 8. The device ofclaim 1, further comprising: a first detector operative to detect forpresence of a large amplitude of the jammer signals in the first orsecond multipath signal; a second detector operative to detect for asignal level of a desired signal in the first or second multipathsignal; and a control unit operative to select the first or secondreceive path for use based on outputs of the first and second detectors.9. The device of claim 1, wherein the first and second receive paths areoperable to downconvert the first and second multipath signals directlyfrom radio frequency (RF) to baseband.
 10. The device of claim 1,wherein the first receive path is operable in one of multiple powermodes, each power mode corresponding to different amounts of biascurrent for circuit blocks within the first receive path.
 11. The deviceof claim 10, wherein the first receive path is operable in a low powermode if jammers are not detected or have low amplitude.
 12. The deviceof claim 1, wherein power consumption of the second receive path is lessthan fifty percent of power consumption of the first receive path. 13.The device of claim 1, wherein power consumption of the second receivepath is less than power consumption of the first receive path.
 14. Adevice including a wireless diversity receiver characterized by a firstand second receive path circuits each operable to downconvert a desiredsignal transmitted from a common source and received by at least twoantennas, the second receive path implemented with circuit blocks thatinherently consume less power than the circuit blocks of the firstreceive path, the first and second receive path circuits areinterdependently alternatively enabled based directly on a detectedpresence of jammer signals out-of-band and independently associated withat least one of the first multipath signal and the second multipathsignal.
 15. The device of claim 14, wherein the first and second receivepath units are selectably enabled by a control unit based on whether ornot jammers may be present or have low amplitude.
 16. The device ofclaim 14, wherein power consumption of the second receive path circuitis less than fifty percent of power consumption of the first receivepath circuit.
 17. The device of claim 14, wherein the device is anintegrated circuit.
 18. The device of claim 14, wherein the device is amobile device.
 19. A device including a wireless diversity receivercharacterized by a first and second receive path circuits each operableto downconvert a desired signal transmitted from a common source andreceived by at least two antennas, the second receive path implementedwith circuit blocks that inherently consume less power than the circuitblocks of the first receive path, the device further comprising: adetector to detect the presence of large amplitude jammer signals in thedesired signal; and a control unit to enable the first and secondreceive path circuits, the first and second receive path circuits areinterdependently alternatively enabled based directly on a detectedpresence of jammer signals out-of-band and independently associated withat least one of the first multipath signal and the second multipathsignal.
 20. The device of claim 19, wherein the detector determines whenjammers are not present or have low amplitude.
 21. The device of claim19, wherein power consumption of the second receive path circuit is lessthan fifty percent of power consumption of the first receive pathcircuit.
 22. The device of claim 19, wherein the device is an integratedcircuit.
 23. The device of claim 19, wherein the device is a mobiledevice.
 24. In a device configured for diversity mode operation andincluding at least two antennas and characterized by at least a firstreceive path circuit having high power circuit blocks and a secondreceive path circuit having low power circuit blocks, a method todownconvert a desired signal transmitted from a transmit antenna andreceived by the least one antenna, comprising: identifying, by a controlunit, when a signal level of the desired signal is such that it can beprocessed by low circuit blocks, the second receive path implementedwith circuit blocks that inherently consume less power than the circuitblocks of the first receive path, the first and second receive paths areinterdependently alternatively enabled based directly on a detectedpresence of jammer signals out-of-band and independently associated withat least one of the first multipath signal and the second multipathsignal; downconverting, by the second receive path circuit, the desiredsignal using low power circuit blocks in response to being enabled bythe control unit; and downconverting, by the first receive path circuit,the desired signal using high power circuit blocks in response to beingenabled by the control unit.
 25. The method of claim 24, furthercomprising receiving enable signals from the control unit based onwhether or not jammers may be present or have low amplitude.
 26. Themethod of claim 24, wherein power consumption of the second receive pathcircuit is less than fifty percent of power consumption of the firstreceive path circuit.
 27. The method of claim 24, wherein the device isan integrated circuit.
 28. The method of claim 24, wherein the device isa mobile device.
 29. A device configured for diversity mode operationand characterized by a first receive path means and second receive pathmeans for downconverting a desired signal, transmitted from a commonsource to at least two antennas, in low power mode and in high powermode, respectively, the device further comprising: means for identifyingwhen a signal level of the desired signal is above a desired level, thesecond receive path implemented with circuit blocks that inherentlyconsume less power than the circuit blocks of the first receive path,the first and second receive path means are interdependentlyalternatively enabled based directly on a detected presence of jammersignals out-of-band and independently associated with at least one ofthe first multipath signal and the second multipath signal; means fordownconverting, by the second receive path means, the desired signalusing low power in response to being enabled by the means foridentifying; and means for downconverting, by the first receive pathmeans, the desired signal using high power circuit blocks in response tobeing enabled by the control unit.
 30. The device of claim 29, furthercomprising means for processing a different multipath of the desiredsignal concurrently at least when the signal level is not below thedesired level.
 31. The device of claim 29, further comprising means forgenerating enable signals to the first and second receive path meansbased on whether or not jammers may be present or have low amplitude.32. The device of claim 29, wherein power consumption of the secondreceive path means is less than fifty percent of power consumption ofthe first receive path means.
 33. The device of claim 29, wherein thedevice is an integrated circuit.
 34. The device of claim 29, wherein thedevice is a mobile device.